1. Field of the Invention
This invention relates to superconducting type II palladium alloy hydride compositions and to superconducting electrical devices containing these materials.
2. Description of the Prior Act
The major superconducting type II materials of interest exhibit critical temperature T.sub.c values greater than about nine degrees kelvin (9.degree. K.), upper critical field strength H.sub.c values greater than about 8 teslas (8T), and critical current density (J.sub.c) values greater than about 10,000 amperes per square centimeter (10.sup.4 amps./cm..sup.2).
Two classes of materials--inherently brittle niobium-tin (Nb.sub.3 Sn) compounds described, e.g., by Buehler et al in U.S. Pat. No. 3,124,455, and ductile niobium-titanium (Nb.sub.0.40 Ti.sub.0.60) alloys described, e.g. by Matthias in U.S. Pat. No. 3,167,692--are generally employed as superconducting materials in composite form with normally conducting low resistance metals in high-performance superconducting magnets and/or other electrical devices requiring high current density while immersed in high magnetic fields. These superconducting materials in film, filament, strand or wire forms are embedded in a normally conducting matrix material such as copper, in order to protect the electrical device in the event of entry of the Nb.sub.3 Sn or Nb.sub.0.40 Ti.sub.0.60 material into a normal conducting high resistance state. To further protect these devices from the effects associated with a normal resistance state at critical current densities various complex manufacturing techniques, e.g. those described by Shattes et al U.S. Pat. No. 3,710,000, are employed in the fabrication of multifilamentary superconducting type II alloy and compound composites. These multifilament composite materials reduce the risk of deleterious heat spike effects caused by flux jumps, conductor motion, and screening currents induced with internal field changes. Superconducting niobium-titanium alloy filament diameters, e.g. about 10 micrometers, can be used to reduce the effects of dynamic losses associated with electrical devices experiencing screening-current rapid field changes. Eddy current loss effects are minimized by twisting and transposing superconducting filaments embedded in copper cells and by isolating these cells from other cells by thin copper-nickel insulating walls.
Manufacturing techniques associated with the fabrication of fine filamentary superconducting structures using niobium-tin and related A15 compounds are more complex than the manufacturing procedures associated with the use of niobium-titanium alloys. Illustratively niobium-tin conductors are prepared by compacting mixtures of niobium and tin powders inside a niobium tube with subsequent drawing of the tube into a length of wire. The niobium-tin compound is then formed by heat treatment only after the wire has been installed in the electrical device so that the effects of flexing and bending are minimized in the use of these extremely brittle compounds. Wire drawing of a pure niobium metal rod embedded in a matrix of bronze (an alloy of copper and tin) to final size with subsequent heating of the wire causing some of the tin to migrate from the bronze into the niobium where it reacts to form the desired niobium-tin superconductor is another useful fabrication method. However, notwithstanding these improved manufacturing techniques the highly brittle nature of the resulting niobium-tin superconductors continues to limit their use even though their high critical temperature T.sub.c of about 18.degree. K. characteristics reduce refrigeration costs associated with cryogenic superconducting systems.
The palladium alloy hydride superconducting materials described herein can be manufactured in the form of ductile films, fibers, strands, and wires that exhibit critical current density J.sub.c, comparable critical field strength H.sub.c or comparable critical magnet induction B.sub.c, respectively, and critical temperature T.sub.c characteristics generally heretofore only associated with inherently brittle niobium-tin (Nb.sub.3 Sn) type A15 superconducting materials. The palladium alloy hydride materials are especially useful in the manufacture of electrical devices which require high J.sub.c critical current density and/or high critical field strength H.sub.c and high critical temperatures T.sub.c including for example, superconducting power transmission cables, high horsepower superconducting direct current motors and generators--especially homopolar type machines, alternators with superconducting rotors, superconducting magnets used for the storage of electrical power, "SADDLE" type magnets used in magnetohydrodynamic (MHD) power generators as well as toroidal magnets useful in the generation of power by thermonuclear fusion reactors.